1. Field of the Invention
The present invention relates to a vertical-to-surface transmission electrophotonic device and, more particularly to a vertical-to-surface transmission electrophotonic device used in massive and parallel optical transmission and optical information processing.
2. Description of the Prior Art
A vertical-to-surface transmission electrophotonic device performs light emission and light reception on the same structure (Japanese Patent Application Laid-Open No. Hei 4-101483).
FIG. 1 is a sectional view showing a vertical-to-surface transmission electrophotonic device of a vertical cavity type as an example of the conventional vertical-to-surface transmission electrophotonic device. A guide layer and a distributed Bragg reflector are formed on the upper and lower surfaces of a quantum well layer operated as a light-absorption/active layer. The vertical cavity type vertical-to-surface transmission electrophotonic device has a "pnpn" structure.
As shown in FIG. 2 , in an optical integrated element described in CONFERENCE RECORD OF OPTICAL COMPUTING, PP. 164-166, 1990, a light-emitting portion (microlasers or .mu.-lasers) and a light-receiving portion (detectors) are independently formed to optimize the characteristics of these portions.
This conventional vertical cavity type vertical-to-surface transmission electrophotonic device must have a high reflectance of the distributed Bragg reflector to obtain a high Q value during resonance because the threshold current value of laser emission is decreased. For this reason, when this element is used as a light-receiving element, a detector bandwidth becomes narrow, and durability (tolerance) against variations in lasing wavelength due to the non-uniform film thickness between elements and the increase in temperature is poor, resulting in inconvenience. Another optical integrated element having a structure in which light-emitting and light-receiving portions are separated from each other is also proposed, as shown in FIG. 5. It is difficult to form a conventional surface emission type laser and a light-receiving element on a single substrate due to their structural difference. Any practical device having both the surface emission type laser and the light-receiving element on the single substrate has not yet been proposed.